The most malignant category of WHO Grade four included both IDH-mutant glioblastoma and IDH-wildtype glioblastoma, which was problematic as the IDH-mutant glioblastomas were “secondary” and usually transformed from lower grade gliomas with better outcomes than the IDH-wildtype “primary” glioblastomas that arose de novo. This evidence concerns the gene IDH1 and central nervous system cancer.